Carlos F Pena Malacara

Carlos F Pena Malacara

Department of Cellular Engineering and Biocatalysis
Institute of Biotechnology
National Autonomous University of Mexico

Title: Changes of the mean molecular mass of polyhydroxybutyrate (PHB) synthesized by the OP strain of Azotobacter vinelandii cultured under different oxygen transfer conditions


Carlos Pena-Malacara got his PhD at National University of Mexico (UNAM). He is currently Titular Professor in the Department of Cellular Engineering and Biocatalysis in the Biotechnology Institute (UNAM) and member of the National System of Researchers. Dr. Pena has been visiting professor in the Oviedo University, Spain, in the RWTH-Aachen in Germany and in the Catolic University of Valaparaiso in Chile. He has more than 30 publications, 4 book chapters and is editor of a book in the area of fermentation technology. Since several years ago Prof Pena have studied the fermentation factors, which control the synthesis and composition of bacterial alginate and polyhydroxybutirate (PHB).


Poly-β-hydroxybutyrate (PHB) is an intracellular polyester of the polyhydroxyalkanoates (PHAs), a family of storage polymers produced by numerous bacteria, including Azotobacter vinelandii Azotobacter. Mechanical properties and therefore the applications of PHB depends on the molecular mass (MM) of this polymer. Previous studies have shown that the molecular mass of PHB produced by species of Azotobacter could be altered by the medium composition and the aeration conditions The objective of present study was to evaluate the effect of the oxygen transfer rate (OTR) on the MM of PHB accumulated by the strain OP of A. vinelandii overproducing PHB and unable to synthesize alginate. Cultures were developed in 3 L fermenter, containing PY sucrose medium, keeping constant the pH at 7.2 and the temperature at 29oC. OTRmax was manipulated through controlling the agitation rate and gases mixture (oxygen-nitrogen). MM of PHB was determined by HPLC-GPC (gel permeation chromatography) with chloroform as mobile phase and using polystyrene standards. Results revealed that, independently of the OTRmax established in the culture, the mean molecular mass of PHB was between 4,800 to 5,200 kDa in the range of 4 to 32 mmol L-1 h-1. The more important differences in the molecular mass were observed with the age of the culture, finding that the MM of PHB decreased around 1,000 kDa, at the end of the exponential growth phase. This behavior could be caused by depletion of some essential nutrient (different to sucrose) or the accumulation of a metabolite, which promotes the degradation of PHB by the action of the depolymerases.